ebt_among is special, it has a dynamic match size and is exempt
from the central size checks.
commit c4585a2823edf ("bridge: ebt_among: add missing match size checks")
added validation for pool size, but missed fact that the macros
ebt_among_wh_src/dst can already return out-of-bound result because
they do not check value of wh_src/dst_ofs (an offset) vs. the size
of the match that userspace gave to us.
NB: Fixes tag is intentionally wrong, this bug exists from day
one when match was added for 2.6 kernel. Tag is there so stable
maintainers will notice this one too.
Tested with same rules from the earlier patch.
Fixes: c4585a2823edf ("bridge: ebt_among: add missing match size checks")
Reported-by: <syzbot+bdabab6f1983a03fc009@xxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
---
Paolo, if you have time it would be great if you could
double-check that the tests in place are now sufficient
and there aren't any more bugs lurking in this thing.
Thanks!
net/bridge/netfilter/ebt_among.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/net/bridge/netfilter/ebt_among.c b/net/bridge/netfilter/ebt_among.c
index c5afb4232ecb..93f1b267d2ea 100644
--- a/net/bridge/netfilter/ebt_among.c
+++ b/net/bridge/netfilter/ebt_among.c
@@ -177,6 +177,22 @@ static bool poolsize_invalid(const struct ebt_mac_wormhash *w)
return w && w->poolsize >= (INT_MAX / sizeof(struct ebt_mac_wormhash_tuple));
}
+static bool wormhash_offset_valid(int off, unsigned int len)
+{
+ unsigned int alleged_off;
+
+ if (off == 0) /* not present */
+ return true;
+
+ if (off < 0)
+ return false;
+
+ alleged_off = off;
+ alleged_off += sizeof(struct ebt_mac_wormhash);
+
+ return alleged_off <= len;
+}
+
static int ebt_among_mt_check(const struct xt_mtchk_param *par)
{
const struct ebt_among_info *info = par->matchinfo;
@@ -189,6 +205,10 @@ static int ebt_among_mt_check(const struct xt_mtchk_param *par)
if (expected_length > em->match_size)
return -EINVAL;
+ if (!wormhash_offset_valid(info->wh_dst_ofs, em->match_size) ||
+ !wormhash_offset_valid(info->wh_src_ofs, em->match_size))
+ return -EINVAL;
+
wh_dst = ebt_among_wh_dst(info);
if (poolsize_invalid(wh_dst))
return -EINVAL;
--
2.16.1
--
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